Rename ssl_set_bio_timeout() to set_bio()

Initially thought it was best to keep the old function around and add a new
one, but this so many ssl_set_xxx() functions are changing anyway...

ChangeLog

diff --git a/ChangeLog b/ChangeLog
index cf834d3..8616934 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -41,7 +41,8 @@
      (support for renegotiation now needs explicit enabling in config.h).
    * net_connect() and net_bind() have a new 'proto' argument to choose
      between TCP and UDP, using the macros NET_PROTO_TCP or NET_PROTO_UDP.
-   * ssl_set_bio() now requires that p_send == p_recv.
+   * ssl_set_bio() changed signature (contexts merged, order switched, one
+     additional callback for read-with-timeout).
    * Some constness fixes
 
 Removals
@@ -62,7 +63,6 @@
 New deprecations
    * md_init_ctx() is deprecated in favour of md_setup(), that adds a third
      argument (allowing memory savings if HMAC is not used)
-   * ssl_set_bio() is deprecated in favour of ssl_set_bio_timeout().
 
 Semi-API changes (technically public, morally private)
    * Changed md_info_t into an opaque structure (use md_get_xxx() accessors).
@@ -88,6 +88,10 @@
    * The NET layer now unconditionnaly relies on getaddrinfo().
    * Compiler is required to support C99 types such as long long and uint32_t.
 
+Changes from the 1.4 preview branch
+   * ssl_set_bio_timeout() was removed, split into mbedtls_ssl_set_bio() with
+     new prototype, and mbedtls_ssl_set_read_timeout().
+
 = mbed TLS 1.3 branch
 
 Security